Photolysis of tetrazoles and tetrazolides



United States Patent O US. Cl. 204-158 21 Claims ABSTRACT OF THEDISCLOSURE A tetrazole is subjected to specified electromagneticradiation to photolyze the same to nitrogen gas and a reactive1,3-dipolar intermediate, and the intermediate is converted into a ringcompound. A tetrazole can be converted to a tetrazolide and the lattercan then be subjected to the radiation.

BACKGROUND OF THE INVENTION (1) The field of the invention comprises thephotolysis of tetrazoles and tetrazolides.

(2) While the thermal decomposition of various tetrazoles has beenreported, the photolysis of these compounds has not, so far as is known,been described. The photolytic reactions of tetrazolides are alsobelieved to be new.

SUMMARY OF THE INVENTION Useful organic compounds are preparedphotochemi cally by subjecting tetrazoles or tetrazolides to ultravioletradiation, preferably in the presence of an unsaturated non-aromaticcompound. The photolysis of the tetrazole or tetrazolide leads to areactive intermediate, and the non-aromatic compound is capable oftaking part in an addition reaction involving such intermediate, leadingto various organic compounds of interest. The described photochemicalreaction is performable at low temperatures and in the substantialabsence of side reactions; and owing to the variety of the reactantsthat may take part therein, is capable of producing a broad array ofproducts. Some of these products are of value as light stabilizers forlight-unstable materials; for example, certain lubricating oil fractionsmay be improved in respect of their resistance to light and air. Otherproducts may act as optical brighteners.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS Any suitable tetrazole may bephotolyzed, including tetrazole itself and substituted tetrazoles.Referring to tetrazole, two tautomeric structures are known:

( NZN In 1,2,3,4-tetrazole, substitution is possible at the 1 and 5positions, and in 2,l,3,4-tetrazole at the 2 and 5 positions. Forpurposes of the invention, the preferred substituting groups arehydrogen, alkyl, aryl, substituted alkyl, and substituted aryl, althoughany other suitable group is acceptable, including acyl, acyloXy, amino,amido, aryloxy, alkoxy, carbalkoxy, cycloalkyl, halogen, hydroxy,cyanide, keto, mercapto, nitrate, nitro, sulfide, sulfonyl, vinyl,trialkylsilyl, etc. One or two of these groups, either the same ordifferent, may be present in the tetrazole, and will be present in theresulting product. For convenience, the term hydrocarbyl group may beused to designate any group containing only carbon and hydrogen, such as3,528,897, Patented Sept. 15, 1970 "ice alkyl, aryl, alkenyl, alkynyl,alkaryl, aralkyl, etc.; and the term organyl may be used to designatehydrocarbyl groups, substituted hydrocarbyl groups, and heterocyclicgroups.

Suitable specific illustrative substituted tetrazoles include thefollowing (the numbering of the N atoms in the tetrazole ring areomitted for convenience):

l-methyland 2-methyltetrazoles l-ethyltetrazole l-, 2-, andS-phenyltetrazoles 1- and S-hydroxytetrazoles S-methyl-l-phenyltetrazole1,5-diphenyltetrazole 2,5-diphenyltetrazole l,S-pentamethylenetetrazoleS-hydroxy-l-phenyltetrazole S-methylthiotetrazoleS-methylsulfonyltetrazole S-aminotetrazole S-chlorotetrazole5-para-anisyltetrazole 5-( l-phenanthryl -1-phenyltetrazole 1, andZ-naphthyltetrazoles 1,5-di-beta-naphthyltetrazole The tetrazolecompound is preferably in the liquid phase during irradiation. If it isnot normally a liquid compound, it may be heated above its melting pointto liquefy the same; or, as is preferable, it is dissolved in a suitablesolvent. If the compound is heated, it is desirable to select compoundsof low melting point to avoid thermal reactions. As to the solvent, itmay be inert with respect to the tetrazole photolysis product, or it maybe reactive therewith; in the latter case the solvent comprises theabovenoted unsaturated non-aromatic compound. Whether in ert orreactive, the solvent should not react with the starting tetrazole.

Where the solvent is inert, it is found that the tetrazole undergoesdimerization. The following equation, involving photolysis ofS-phenyltetrazole (I), may illustrate this reaction:

Ph N N 9 N 1 I l HN/ \N V N2+N I o N NH 1 0 11 lLh c l h (I) Under theinfluence of the radiation, the starting tetrazole (I) is converted to areactive 1,3-dipolar intermediate, believed to be represented by (II),which dimerizes to form (HI), namely,3,6-diphenyl-dihydro-1,2,4,5-tetrazine. The latter may undergo oxidationto 3,6-diphenyl- 1,2,4,5-tetrazine, a bright purple-colored compound.The radiation consists essentially of one or more wave lengths in therange of 1000 to 6000 angstrom units. The preferred radiation isultraviolet having a wave length in the range of 1000 or 2000 to 3850angstrom units. In terms of light flux, this may vary from 10 to 10photons absorbed per hour per sq. cm. of mixture undergoing photolysis.Any suitable source of radiation may be used, such as a Hanoviaphotochemical lamp, Type A, of 550 Watts, or a Delmar ScientificLaboratories lamp, model DM-580, and the like. If desired, the lamp maybe suitably equipped to isolate a desired wave length. Flourescent lampsare useful, as well as sunlight and a laser 'beam. Flash photolysis maybe used. Distances between the light source and the reaction mixture areconventional, e.g., 1 to 10 or more inches; and preferably air isexcluded from the mixture. The latter, of course, is held in a vesselthat will transmit the desired radiation. During application of theradiation, it is preferred to maintain the mixture at or near roomtemperature, and if necessary, cooling is used. The time of exposure isvariable, but generally may extend from one or more hours to one or moredays. Besides nitrogen, substantially the only other product of thephotolysis is the dimer. As one mole of nitrogen is evolved per mole oftetrazole photolyzed, the amount of nitrogen may be used to determinethe extent of completion of the reaction.

Sutiable inert solvents for carrying out the dimerization includeethers, saturated hydrocarbons, and aromatic hydrocarbons. Also suchcompounds as p-dioxane, methyl acetate, ethyl acetate, tetrahydrofuran,etc. Although some of the latter compounds, such as the aromatics, areunsaturated, their multiple bonds are not reactive in the environment,i.e., they do not take part in the described addition reaction.

Where the solvent for the tetrazole is reactive, as is the case withunsaturated non-aromatics, i.e., compounds having a multiple bond thatis reactive in the environment,

an addition reaction is possible between the intermediate I and thesolvent. For example, using an olefin,

RCH=CHR as solvent, the following equation may be written involving theintermediate (II) of Equation I:

The intermediate adds across the double bond of the olefin, forming aring compound (IV) (3-phenyl-delta pyrazoline, if R is H). The radicalsR of the olefin may be hydrogen, alkyl, aryl, alkaryl, aralkyl, etc. Theolefin may be said to trap the intermediate, being thus designatable asa trapping agent. The olefin may be a linear one, or cyclic, orpolycyclic, and may have one, two, or more double bonds.

A large number of reactive solvents for the tetrazole compound areavailable, all of which are characterized by having at least onereactive multiple bond connected to a carbon atom. They are chosen fromnon-aromatic compounds, including aliphatic, alicyclic, or heterocycliccompounds. As indicated, aromatics are considered to have double bondsthat are non-reactive in the environment; however, aromatics having anunsaturated side chain may be useful, and in this case the compound isconsidered to fall in one of the above-mentioned groups. The usefulcompounds include those having carbon-tocarbon unsaturation, such asolefins RCH=CHR, actaylenes RCk-CR, allenes RCH=C=CHR, conjugated dienesRCH=CH-CH=CH ketenes RCH= =0, unsaturated esters RCH=CHCOOR anddiesters, and vinyl derivatives like vinyl ethers RCH CHOR, and vinylamides RCH=CN(R)COR; those having carbon-tonitrogen unsaturation, suchas nitriles RCEN, azomethines The photolysis products of these reactivesolvents may be indicated briefly. Thus, delta -pyrazolines, illustratedin Equation (2), are obtainable from olefins, conjugated dienes,allenes, unsaturated esters, enamies, vinyl ethers, and vinyl amides;more particularly, conjugated dienes lead to 5-vinyl-delta -pyrazolines,allenes to S-methylenedelta -pyrazolines, unsaturated esters toS-carboalkoxydelta -pyrazolines, unsaturated to diesters to4,5-dicarboalkoxy-delta -pyrazolines, enamines to 5-amin0-deltapyrazolines, vinyl ethers (Where 2 is alkyl) to S-alkoxydelta-pyrazolines, and vinyl amides to 5-acylaminodelta -pyrazolines.Acetylenes give pyrazoles N N\\\ (I:

aldehydes and ketones give delta -1,2,4-oxadiazolines thioketones givedelta -1,2,4-thiadiazolines.

1i Y:- N\

nitriles give triazoles,

azomethines give triazolines Ilr I N I /N o I isocyanates may givetriazolin-4-ones and isothiocyanates may give triazolin-4-thiones K Q4;, l

The reactive compound or trapping agent need not necessarily be asolvent for the tetrazole, as it is possible to dissolve the tetrazolein an inert or non-reactive solvent in which the reactive trapping agentis also soluble. One of the described inert solvents may be selected forthis purpose, only a simple test being necessary to determine whichsolvent is suitable.

As indicated, the photolysis is preferably done at room temperature,although higher and lower temperatures, ranging from about 0 to or C.,are also suitable.

At these temperatures the reaction mixture is in the liquid phase, as ispreferred, Separation of the desired reaction product may beaccomplished by any suitable conventional technique. Yields of desiredproduct, based on the starting tetrazole, may range up to 80%, or evenup to 95%, mole basis.

The products obtained by photolyzing an aryltetrazole in the presence ofan unsaturated ester are of use as light stabilizers for hydrocarbonfractions subject to darkening on exposure to light. These products,which may be used in conventional stabilizing amounts, are carboalkoxyaryldelta -pyrazolines, where the aryl group or groups may be phenyl,tolyl, xylyl, naphthyl, and the like, the alkoxy group may be methoxy,ethoxy, propoxy, butoxy, etc., and where one or more carboalkoxy groupsmay be present. The hydrocarbon fraction is preferably a higher boilingmaterial, such as one in the lubricating oil range, containing partiallyhydrogenated polynuclear aromatics, which are thought to be responsiblefor the light instability of the fraction. Other light-unstablefractions may also be benefitted, as well as other light-unstablematerials whether containing hydrocarbons or not. thestabilizercontaining fraction may exhibit two or more times the lightresistance as the same fraction without stabilizer.

Aryl-delta -pyrazolines, and derivatives thereof, are also of value asoptical brighteners, and may be added in small amounts to materials,such as textile fibers and fabrics, particularly synthetics, whichnormally are not pure white, appearing more or less yellowish, butwhich, with addition of the brightener, acquire increased whiteness. Thearyl-delta -pyrazolines fluoresce in the visible blue region, a factbelieved to account for their brightening power. Other materials thatmay be brightened are various chemical coatings, plastics, paper, andsoap. In the case of plastics, it is contemplated that the brighteningagent be added to the reaction mixture for producing the polymer productin order to effect a chemical bonding of the agent to the polymerchains. An ester derivative like carboalkoxy aryl-detla -pyrazoline mayalso be of use for maknig resins of the polyester type, as by reactingthe derivative with a glycol like ethylene glycol; the derivative wouldthus replace, or substitute for, dibasic acids of the type ofterephthalic acid.

An increased variety of products is possible by first converting thestarting tetrazole to a tetrazolide and then subjecting the resultingreaction mixture to photolysis. For example, if S-phenyltetrazole is thestarting tetrazole, it is dissolved in methanol and treated with sodiummethoxide, thus forming sodium tetrazolide:

Ne H (VI) (VII) (4) The formula of intermediate (VI) is speculative, butas shown in Example 6, the ether product (VII) is identifiable. Thestructure of the ether depends on the alcohol used as solvent and on thegroup in the 5-position of the starting tetrazole, and as thesevariables are each of considerable scope, it may be seen that a widevariety of ethers may be synthesized. Thus, the group in the 5- positionmay be any of those already indicated; and any alcohol may be used thatis capable of dissolving the tetrazole, including aliphatic, aromatic,and cycloaliphatic alcohols. It will be understood that treatment of thestarting tetrazole may utilize various alkali and alkaline earth metalalkoxides besides sodium methoxide; the latter, however, is a veryuseful strong base. It is also possible to isolate the tetrazolide fromthe reaction mixture and irradiate it separately.

Furthermore, by using other reactive solvents instead of alcohols, aneven greater diversity of products is possible. Thus, amines may be usedas the reactive solvent, including alkyl, cycloalkyl, aryl, andheterocyclic amines. Olefins, such as those described, or other usefulsolvents, and aliphatic and cyclic thiols.

The invention may be illustrated by the following examples.

Example 1 Illustrating the photolysis of S-phenylterazole to form thedimer, 0.6 g. of the tetrazole was dissolved in 50 ml. oftetrahydrofuran (THF) and the solution placed in a quartz tube. The THFfunctioned as a non-reactive solvent. The tube was irradiated withultraviolet radiation, using a Hanovia 450-watt medium pressure mercuryvapor lamp, at 25 C. The photolysis was followed by determining theamount of nitrogen evolved, one mole of nitrogen corresponding to onemole of tetrazole photolyzed. After 30 hours, the recation was 75%complete, and after 72 hours, it was 99.8% complete. A clear yellowsolution formed which was evaporated under reduced pressure to removethe solvent, giving 0.55 g. of a yellow solid having no sharp meltingpoint. This product was dissolved in ethanol, and air was bubbled for 3hours through the solution, which became a deep red. After evaporationof the solvent, 0.5 g. of a red-blue solid was obtained; onrecrystallization from ethanol, crystals melting at about 185 C.resulted, comprising 3,6-diphenyl-1,2,4,5-tetrazine.

Example 2 Photolysis of a tetrazole with an olefin was carried out bymixing 0.48 g. of 2,5-diphenyltetrazole with 40 ml. ofalphadicyclopentadiene, a reactive solvent, and irradiating the mixturein a quartz tube for 17 hours with the lamp described in the precedingexample. The resulting solution was evaporated by placing it on a hotwater bath and reducing the pressure to 1 mm. by means of a vacuum pump.A gummy yellow solid was obtained which was recrystallized from ethanol,giving 0.34 g. of a crystalline solid, 111. 171174 C. The product wasthought to be 1,3- diphenyl 4,8 methano 3a.4.4a.7a.8.8ahexahydro-indeno-(5,6-c) pyrazole:

Example 3 Photolysis of a tetrazole in the presence of an unsaturatedester was per-formed by dissolving 1 g. 2,5-diphenyltetrazole and 8 g.dimethyl fumarate in a non-reactive solvent comprising 30 ml.tetrahydrofuran and ml. ethyl acetate. The mixture was placed in aquartz tube and then irradiated with light of 254 millimicron Wavelength in a Rayonet chamber reactor for 35 hours at a maximumtemperature of about 35 C. This reactor, which is made by Southern NewEngland Ultraviolet Co., Middletown, Conn., contained 16 low pressuremercury lamps 84% of whose emission is at 254 millimicrons. Theirradiated product was a yellow solution which after evaporation of thesolvent gave 2.2 g. of a crude solid. The latter was recrystallizedtwice from methanol, giving yellow crystals (plates), 15l-152.5 C. Itsanalysis was determined to be C H N 'O and it was identified as trans4,5 dicarbornethoxy 1,3 diphenyl delta pyrazoline.

Example 4 The photolysis of the preceding example was repeated, exceptthat the unsaturated ester was diethyl fumarate, in an amount of 227 g.,and the tetrazole was used in an amount of 29.4 g. No solvent was usedas the ester was in liquid state and able to dissolve the tetrazole.=Irradiation in the Rayonet chamber was carried out for 3 days, leadingto a yellow liquid product. After evaporation of excess fumarate, anoily product resulted which after two recrystallizations from methanolled to a solid, M. 72.5-73.5 *C. The yield was 34.5 g. It was determinedto be trans-4,S-dicarboethoxy-l,3-diphenyl-delta -pyrazoline.

Example 5 2,55-diphenyltetrazole in an amount of 1.0 g. was photolyzedwith 30 ml. dimethyl maleate in the Rayonet reactor. The inert solventcomprised 5 ml. n-hexane and 20 ml. tetrahydrofuran. The reaction wascomplete after 15 hours, but irradiation was performed for a total of22.5 hours. The resulting clear viscous yellow solution was evaporatedto remove solvent, giving 2.0 g. of a product. After severalrecrystallizations from methanol, a crystalline product was obtained, M.l51l52.5 C. It was the same product obtained in Example 3.

Example 6 5-phenyltetrazole was convertel to the tetrazolide andirradiated. The tetrazole in an amount of 0.6 g. Was dissolved in 50 ml.methanol containing 3 g. sodium methoxide; the tetrazolide (sodiumS-phenyltetrazolide) formed in this step and dissolved in the methanol.The mixture was placed in a quartz tube and irradiated for 69 hours,using the lamp described in Example 1. The solution was then evaporated,giving 3 g. of an amorphous solid. To it were added 15 ml. water, andthe resulting suspension was extracted 3 times with IO-ml. portions ofether. The ether extracts were combined and dried over anhydrous MgSOthen filtered, and the ether evaporated ofl. About 0.1 g. of a paleyellow oil was obtained which was identified by vapor phasechromatographic analysis as benzyl ether.

0n repeating the foregoing, the tetrazolide, a thermally stablecompound, was isolated before subjecting it to irradiation, and thelatter step was carried out as described. The same ether product wasobtained.

Example 7 The photolysis product of Example 3 was tested as a lightstabilizer in a lubricant produced by hydrocracking and known to containpartially hydrogenated polynuclear aromatics having three or morearomatic rings. The amount of such product used was 0.1% by weight, andat the same time another portion of the same lubricant was tested butwithout stabilizer. After exposure of both lubricants to light and airunder the same conditions, it was found that in the case of thestabilized lubricant the time required for darkening was extended by 2to 3 times by comparison with the unstabilized lubricant. In acontinuation of these tests, some 120 additives were tried forlight-stabilizing properties but without eifect.

It will be understood that the invention is capable of obviousvariations without departing from its scope.

In the light of the foregoing description, the following is claimed.

1. Method of preparing organic compounds photochemically comprisingexposing a tetrazole to electromagnetic radiation of a wave length of1000 to 6000 angstrom units for a time suflicient to photolyze saidtetrazole to produce nitrogen gas and to form a reactive 1,3-dipolarintermediate, and continuing said photolysis to form a ring compound ofsaid intermediate.

2. Method of claim 1 wherein said further reaction step comprisesdimerizing said intermediate during said photolysis.

3. Method of claim 1 wherein said further reaction step comprises anaddition reaction, carried out during said photolysis, in the presenceof a non-aromatic compound having at least one multiple bond connectedto a carbon atom, whereby said intermediate adds across said multiplebond of said compound.

4. Method of claim 3 wherein said multiple bond is a triple bond and theaddition product is a pyrazole derivative.

5. Method of claim 3 wherein said non-aromatic compound has a C to 0multiple 'bond and the addition product is an oxadiazole derivative.

6. Method of claim 3 wherein said non-aromatic compound has a C to Smultiple bond and the addition product is a thiadiazole derivative.

7. Method of claim 3 wherein said unsaturated nonaromatic compound isselected from olefins, conjugated dienes, allencs, ketenes, acetylenes,aldehydes, ketones, thioketones, nitriles, azomethines, isocyanates,isothiocyanates, enamines, vinyl ethers, vinyl esters, and vinyl amides.

8. Method of claim 3 wherein said tetrazole substituent is selected fromalkyl, aryl, amino, acyl, alkoxy, amido, alkylthio, alkylsulphonyl,cycloalkyl, aryloxy, hydroxy, halogen, cyanide, nitrate, sulfide,sulfonyl, and mercapto.

9. Method of claim 3 wherein said non-aromatic compound has a C to Nmultiple bond and the addition product is a triazole derivative.

10. Method of claim 9 wherein said compound is a nitrile.

11. Method of claim 3 wherein said non-aromatic compound has acarbon-to-carbon multiple bond.

12. Method of claim 11 wherein said multiple bond is a double bond andthe addition product is a delta -pyrazoline.

13. Method of claim 12 wherein said non-aromatic compound is an olefin.

14. Method of claim 12 wherein said non-aromatic compound is an ester ofa dibasic acid.

15. Method of preparing an organyl derivative from anorganyl-substituted tetrazole comprising converting said tetrazole to atetrazolide in the presence of a reactive solvent for the latter,subjecting the resulting reaction mixture to electromagnetic radiationof a wave length of 1000 to 6000 angstrom units for a time suflicient tophotolyze the tetrazolide, and recovering from the resulting reactionmixture a product incorporating said organyl group and a moiety of saidsolvent.

16. Method of claim 15 wherein said solvent is an alcohol.

17. Method of claim 15 wherein said solvent is an amine.

18. Method of claim 15 wherein said solvent is an olefin.

19. Method of claim 15 wherein said organyl group is a hydrocarbyl groupand said solvent is an alcohol.

20. Method of claim 19 wherein said hydrocarbyl group is an aryl groupand said solvent is an alcohol.

21. Method of claim 15 wherein said tetrazolide is isolated from thereaction mixture before irradiation of the same.

References Cited H WAR WILLIAMS, Primary Examiner my UNITED STATESPATENT OFFICE" CERTIFICATE OF CORRECTION Patent No. 3, 5 97 DatedSeptember 15, 1970 Invenc r( Peter Scheiner It is certified that errorappears in the above-identified patent and that said Letters Patent arehereby corrected as shown below:

Column 2, line 47, intermediate (11) of formula I should be '7 read, inpart,

- instead of Column 3, lines 57-58, J "actaylenes" should be read--acetylenes--.

Column 3, line 67, "isocyanates RN--O--O" should be read --isocyanatesRN====-CO-.

Column L, line "enemies" should be read enamines--.

Column t, line 9, "unsaturated to diesters" should be read --unsaturateddiesters--.

Column L, line 10, "(where 2 is alkyl) should be read --(where R isalkyl)-.

Column 5, line 2, "preferred," should read -preferred.--.

Column 5, line 22, "the" should be read -The--.

L (continued) 3,528,897 Dated September 15, 1970 Patent No.

Invent0r(s) Peter Scheiner PAGE 2 It is certified that error appears inthe above-identified patent and that said Letters Patent are herebycorrected as shown below:

(continued) Column 5, line 60, Formula t) intermediate VII) should beread in part, --PhcH ocH instead of "PhCI-I OCH' Column 6, line 10, "or"should be read --are-.

Column 7, lines 1-4-45, "benz'yl ether" should be read --benzyl methylether--.

Signed and sealed this 8th day of December 1970.

(SEAL) Attest:

WILLIAM E. SCHUYLER, JR.

EDWARD M.FLETCHER,JRI

Commissioner of Patents Attesting Officer

